Chlorofluorocarbons, generally referred to in the industry as CFCs, have been widely used in refrigeration systems. The use of CFCs has been diminishing in recent years because of demands from environmentalists for the reduction if not complete ban of the use of CFCs because of the detrimental effect of CFCs on the atmosphere's ozone layer. Examples of CFCs include CFC-11 which is chlorotrifluoromethane, CFC-12 which is dichlorodifluoromethane, and CFC-113 which is 1, 2, 2-trifluoro-1, 1, 2-trichloroethane. Finding a safe replacement of CFC refrigerants has been a problem which has been difficult to solve. Several replacement candidates have been suggested as alternatives to the fully halogenated hydrocarbons. Examples of safe alternatives include halogenated hydrocarbons containing at least one hydrogen atom such as HCFC-22 which is difluorochloromethane, HCFC-123 which is 1,1-dichloro-2,2,2-trifluoroethane, HFC-134a which is 1,1,1,2-tetrafluoroethane, and HCFC-141b which is 1,1-dichloro-1-fluoroethane.
The ozone depletion potential of these proposed substitutes is significantly less than the ozone depletion potential of the previously used CFCs. Ozone depletion potential is a relative measure of a capability of a material to destroy the ozone layer in the atmosphere. HCFC-22 and HFC-134a generally are recommended as being candidates in refrigerant applications, and HFC-134a is particularly attractive because its ozone depletion potential has been reported as being zero.
The problem with using these alternative materials is that the alternative materials have different solubility characteristics than the CFCs used in refrigerants presently. For example, mineral lubricating oil is incompatible (i.e., insoluble) in HFC-134a. Such incompatibility results in unacceptable compressor life in compressortype refrigeration equipment including refrigerators and air-conditioners including auto, home and industrial airconditioners. The problem is particularly evident in auto air-conditioning systems since the compressors are not separately lubricated, and the mixture of refrigerant and lubricant circulates throughout the entire system.
In order to perform as a satisfactory refrigeration liquid, the mixture of refrigerant and lubricant must be compatible and stable over a wide temperature range such as from about -20.degree. C. and above 80.degree. C. It is generally desirable for the lubricants to be soluble in the refrigerant at concentrations of about 5 to 15% over a temperature range of from -40.degree. C. to 80.degree. C. These temperatures generally correspond to the working temperatures of an automobile air-conditioning compressor. In addition to thermal stability, the refrigeration liquids must have acceptable viscosity characteristics which are retained even at high temperatures, and the refrigeration liquid should not have a detrimental effect on materials used as seals in the compressors.
U.S. Pat. No. 4,755,316, issued to Magid et al, relates to lubricants for refrigeration systems using tetrafluoroethane. The patent describes certain polyoxyalkylene glycols as lubricating oils. Magid et al disclose additives which may be used to enhance performance. Among the additives listed are organic amines.
U.S. Pat. No. 4,559,154, issued to Powell, relates to working fluids for heat pumps of the absorption type. Solvents may be used with the working fluids. Such solvents include ethers, such as tetraglyme, amides which may be lactams such as N-alkyl pyrrolidones, for example N-methylpyrrolidones, sulphonamides, for example tetramethylsulphamide and ureas including cyclic ureas.
U.S. Pat. No. 4,428,854, issued to Enjo et al, relates to an absorption refrigerant composition comprising 1,1,1,2-tetrafluoroethane and an organic solvent capable of dissolving the ethane. N,N-dimethylformamide, N,N-dimethylacetoamide, tetramethylurea, acetonitrile, valeronitrile, N-methylpyrrole, N-methylpyrrolidine, piperidine, N-methylpiperazine, N-methyl-2-pyrrolidone, nitromethane and like nitrogen compound solvents are disclosed as solvents capable of dissolving the ethane.